Replication & Division of Nuclei & Cells (Cambridge (CIE) AS Biology): Flashcards
Exam code: 9700
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- FrontChromosome Structure
Define chromosome.
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Define chromosome.
A chromosome is a structure made of a single, long molecule of DNA wound around histone proteins.
What is the role of histone proteins?
Histone proteins are the proteins that DNA wraps around, helping to package and coil the DNA into a chromosome.
Define sister chromatids.
Sister chromatids are the two identical copies of a chromosome, produced by DNA replication, that are joined together at the centromere.
What is the function of the centromere?
The centromere holds the sister chromatids together and is where the spindle fibres attach during nuclear division.
Define telomere.
A telomere is a region of repetitive DNA found at each end of a chromosome.
The two identical copies of a chromosome joined at the centromere are called .
The two identical copies of a chromosome joined at the centromere are called sister chromatids.
Describe the structure of a chromosome.
A chromosome consists of:
a single, long molecule of DNA
histone proteins that the DNA wraps around
two sister chromatids (after replication) joined at the centromere
a telomere at each end
Define mitosis.
Mitosis is nuclear division that produces two genetically identical daughter nuclei, each with the same number of chromosomes as the parent nucleus.
Why does mitosis produce genetically identical daughter cells?
Because the DNA is replicated before division, so each daughter cell receives an exact copy of the parent cell's chromosomes.
State four processes in which mitosis is important.
Growth of multicellular organisms
Replacement of damaged or dead cells
Repair of tissues by cell replacement
Asexual reproduction
How does mitosis contribute to the growth of an organism?
It increases the number of cells, allowing a multicellular organism to grow larger.
How does mitosis allow asexual reproduction?
It produces genetically identical offspring (clones) from a single parent, without gametes or fertilisation.
Mitosis produces daughter cells that are to the parent cell.
Mitosis produces daughter cells that are genetically identical to the parent cell.
True or False?
Mitosis produces cells that are genetically different from the parent cell.
False.
The daughter cells produced by mitosis are genetically identical to the parent cell.
Define the mitotic cell cycle.
The mitotic cell cycle is the sequence of events in which a cell grows, replicates its DNA and divides to produce two genetically identical daughter cells.
Define interphase.
Interphase is the stage of the cell cycle in which the cell grows and its DNA is replicated.
It consists of the G1, S and G2 phases.
What happens during the S phase of interphase?
DNA replication occurs, so each chromosome is copied to form two sister chromatids.
What happens during the G1 and G2 phases?
The cell grows and makes new organelles and proteins.
G1 occurs before DNA replication and G2 occurs after it.
Define cytokinesis.
Cytokinesis is the division of the cytoplasm to form two separate daughter cells, following mitosis.
State the three main stages of the mitotic cell cycle, in order.
Interphase (G1, S and G2)
Mitosis (nuclear division)
Cytokinesis (division of the cytoplasm)
DNA is replicated during the phase of interphase.
DNA is replicated during the S phase of interphase.
Define telomere.
A telomere is a region of repetitive, non-coding DNA found at the ends of a chromosome.
What is the role of telomeres?
They prevent the loss of genes from the ends of chromosomes during DNA replication.
Why are telomeres needed during DNA replication?
Each round of DNA replication shortens the ends of a chromosome.
Telomeres act as a protective buffer so that no genes are lost.
Telomeres prevent the loss of from the ends of chromosomes during DNA replication.
Telomeres prevent the loss of genes from the ends of chromosomes during DNA replication.
True or False?
Telomeres contain genes that code for proteins.
False.
Telomeres are non-coding, repetitive DNA; they protect the coding genes from being lost.
What could happen to a chromosome that had no telomeres?
Important genes at the ends of the chromosome could be lost each time the DNA is replicated.
Define stem cell.
A stem cell is an unspecialised cell that can divide by mitosis and differentiate into specialised cells.
What is the role of stem cells in the body?
They carry out cell replacement and tissue repair by dividing by mitosis to produce new cells.
Give examples of cells that stem cells continually replace.
Skin cells and red blood cells, which are constantly lost and must be replaced.
Stem cells divide by to replace cells and repair tissues.
Stem cells divide by mitosis to replace cells and repair tissues.
True or False?
Stem cells are specialised cells.
False.
Stem cells are unspecialised; they can divide and differentiate into specialised cells.
Define tumour.
A tumour is a mass of cells that forms as a result of uncontrolled cell division by mitosis.
How can uncontrolled cell division lead to a tumour?
If the cell cycle is not controlled properly, cells divide repeatedly by mitosis, forming a mass of cells called a tumour.
What normally controls the rate of cell division?
Genes that regulate the cell cycle.
If these genes are mutated or damaged, cell division can become uncontrolled.
A tumour forms when cells divide in an way by mitosis.
A tumour forms when cells divide in an uncontrolled way by mitosis.
True or False?
A tumour results from cells that have stopped dividing.
False.
A tumour results from cells dividing in an uncontrolled way, i.e. too much cell division.
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